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Key Findings

The 2011-12 influenza vaccination coverage estimates and key findings reported here are preliminary. These results might differ from final end-of-season coverage estimates which are expected in September, 2012.

Preliminary estimates for the 2011-12 season suggest that:

Overall, 46% of people 6 months and older were vaccinated during the 2011-12 season, a slight increase when compared to the 2010-11 season (Figure 1).

Children: Vaccine uptake for the 2011-12 season was similar for children compared to the 2010-11 season.

Adults: Vaccine uptake for the 2011-12 season increased slightly for adults compared to the 2010-11 season.

Key Limitations

Vaccinated individuals may be more likely to respond to surveys about immunizations than non-vaccinated individuals, individuals may not correctly remember if they (or their children) were vaccinated, and individuals with landline telephones may differ from the general population. Therefore, these surveys likely overestimate influenza vaccination coverage. Using the preliminary coverage estimates, 141 million individuals would have been vaccinated. However, only 132.1 million doses of influenza vaccine were distributed during the 2011-12 season.1 While these telephone surveys likely overestimate vaccination coverage, the results for the 2011-12 season are directly comparable with estimates from the 2010-11 season.

Background

Annual influenza vaccination is the primary way to prevent influenza and its complications2. The severity of influenza varies annually with about:

March 2012 National Immunization Survey (NIS) data for children 6 months through 17 years of age

March 2012 National Flu Survey (NFS) data for adults ≥ 18 years of age

This report summarizes the findings from these surveys and compares March 2012 estimates with results from the March 2011 NIS and NFS. Estimates of vaccination uptake from the March NIS and NFS may differ from final end-of-season coverage estimates. Therefore, the trends reported here may not be reflected in final end-of-season coverage estimates.

Who Received Vaccine?

Coverage estimates for the 2011-12 season were compared with estimates from surveys conducted at the same time during the 2010-11 season. Coverage estimates for age and race/ethnicity subgroups for the 2011-12 season were compared to determine if any differences in vaccination coverage exist by age or race/ethnicity. All differences reported here are statistically significant.

Estimated vaccination coverage with one or more doses for all children was 49.4%, similar to coverage estimates from the same time the previous season (Table 2).

Estimated coverage among children was highest in younger children and was lower in older age groups. Estimated coverage was highest in children 6 to 23 months (67.5%) and lowest among children 5-17 years (45.1%).

Estimated coverage for all child age groups was similar to the previous season.

Estimated coverage was similar among Hispanic (38.8%), non-Hispanic black (35.6%), and non-Hispanic other race (40.3%) adults.

Estimated coverage was higher during the 2011-12 season compared with the same time during the 2010-11 season for Hispanic, non-Hispanic white, and non-Hispanic other race adults. Vaccination coverage among non-Hispanic black adults was similar to the same time the previous season.

Table 5. Estimated influenza vaccination coverage among adults by race and ethnicity, March National Flu Survey

March 2011
% ± 95% CI *

March 2012
% ± 95% CI *

Adults (≥ 18 years)

Hispanic

29.3 ± 7.9

38.8 ± 4.7

Non-Hispanic, White only

44.9 ± 3.6

49.1 ± 1.7

Non-Hispanic, Black only

38.2 ± 11.3§

35.6 ± 4.6

Non-Hispanic, Other or multiple race

28.8 ± 8.6

40.3 + 5.3

* Percentages are weighted to the U.S. population; CI=Confidence Interval half-width

Place of Vaccination

The most common place of vaccination among both adults (32.5%) and children (65.4%) was a doctor’s office (Figure 2). These results are similar to results from the 2010-11 season when 31.6% of adults and 60.2% of children were vaccinated in doctor’s offices.

Other common places of influenza vaccination reported for adults during the 2011-12 season included medically related places besides doctor’s offices (24.7%), pharmacies or stores (19.7%), and workplaces (13.8%). The second most common places of influenza vaccination for children were medically related places other than doctor’s offices (22.7%).

Figure 2. Place of Vaccination for children and adults, March National Flu Survey

What Action To Take?

Although many adults (45.5%) and children (49.4%) were vaccinated during the 2011-12 influenza season, more than half of the United States population ≥ 6 months was not vaccinated against influenza. Continued efforts are needed to increase vaccination coverage, including:

Decrease racial and ethnic disparities: Racial and ethnic disparities remain among adults when compared with non-Hispanic whites. Continued efforts to increase vaccination coverage among adults in other racial and ethnic groups are necessary to decrease these disparities.

National Immunization Survey

The NIS is an ongoing, national landline and cellular list-assisted random-digit-dialed (RDD) telephone survey of households with children who are 19–35 months or 13–17 years (NIS-Teen) at the time of interview. For children 6–18 months and 3–12 years identified during screening households for NIS and NIS-Teen, a short influenza vaccination module was conducted.

Sampling for the NIS is done by list-assisted RDD sampling of both landline and cellular telephones. Sample selection was carried out separately for landline and cellular telephone numbers. Interviews for the March 2012 NIS sample were conducted February 26 through March 31, 2012. Advance letters were sent to landline households for which the telephone number could be matched to an address. The survey interviewers conducted the survey in both English and Spanish; interviews were conducted in other languages using language line interpretation services.

A total of 9,874 NIS frame interviews were completed for children in the March 2012 data set. All estimates were weighted with weights derived based upon the probability of selection of the telephone number, incorporating adjustments for non-response at the telephone number resolution and household screening stages, probability of selecting the child of interest within the household, and for person non-response. The data are also weighted using a ratio adjustment to population controls (age, sex, race/ethnicity, and geographic area).

National Flu Survey

These estimates are based on data from the March 2012 National Flu Survey (NFS) conducted by CDC to rapidly collect influenza vaccination-related data during the 2011-12 influenza season. The purpose of the March survey is to provide rapid estimates of influenza vaccination coverage to inform influenza immunization stakeholders and the public on the progress towards reaching influenza coverage objectives.

The sample was a list-assisted RDD sample of both landline and cellular telephones. Sample selection was carried out separately for landline and cellular telephone numbers. Interviews for the March NFS were conducted March 1 through March 29, 2011. An advance letter was sent to landline households for which the telephone number could be matched to an address. The survey interviewers conducted the survey in both English and Spanish; interviews were conducted in other languages using language line interpretation services. To achieve a higher proportional representation of three racial/ethnic groups – Hispanic, non-Hispanic black, and non-Hispanic Asian – selected geographic areas were oversampled. For the landline sample, selected counties were oversampled, and for the cellular phone sample, selected states were oversampled.

The Council of American Survey Research Organizations (CASRO) response rate was 31.4% for landline and 18.3% for cellular telephones. A total of 12,082 interviews were completed for adults (9,791 from landline and 2,291 from cellular only/mainly households). All estimates were weighted with weights derived based upon the probability of selection of the telephone number (incorporating the oversampling of geographic areas), incorporating adjustments for non-response at the telephone number resolution and household screening stages, probability of selecting the adult/child of interest within the household, and for person non-response. The data are also weighted using a ratio adjustment to population controls (age, sex, race/ethnicity, and geographic area). Top of Page

Limitations

These surveys likely overestimate influenza vaccination coverage. Using the preliminary survey estimates, 141 million individuals would have been vaccinated. However, only 132.1 million doses of influenza vaccine were distributed during the 2011-12 season.1 While these telephone surveys likely overestimate vaccination coverage, the results for the 2011-12 season are directly comparable to estimates from the 2010-11 season.

The 2011-12 influenza vaccination coverage estimates and key findings reported here are preliminary end-of-season estimates and may not be reflected in final end-of-season coverage estimates.

Children 6 months-8 years may require two doses of influenza vaccination to optimize immunity;2 influenza vaccination coverage estimates in this report reflect reported receipt of at least one dose and not whether those children requiring two doses were fully immunized.

NIS and NFS are telephone surveys excluding households with no telephone service. Non-coverage and nonresponse bias may remain after weighting adjustments.

All data rely upon self-report and are not validated with medical records; validity studies have shown that parental report (for children) may overestimate influenza vaccination coverage.

The NFS is a rapid survey with specific focus on influenza vaccination, and thus is also susceptible to nonresponse bias from reduced follow-up time for persons not responding to early call attempts, and self-selection based on the survey topic.